1. Field of the Invention
This invention relates to an abrasive member comprising a non-magnetic substrate and a plurality of abrasive layers, which are overlaid upon the non-magnetic substrate and each of which mainly contains a binder and abrasive grains dispersed in the binder. The abrasive member may take on the form of an abrasive tape, an abrasive disk, or the like, and is used in abrasive processing of materials to be abraded, such as magnetic heads for video tape recorders, audio decks, or magnetic recording and reproducing apparatuses.
2. Description of the Prior Art
As for materials to be abraded, such as magnetic heads, their surfaces are abraded by abrasive members, such as abrasive tapes and abrasive disks, for the purposes of planishing, shape adjustment, or protrusion removal.
Ordinarily, during the process for producing a desired material, the abrasive processing is carried out, in which a predetermined portion of the material is abraded by an abrasive member and is thereby imparted with a desired surface smoothness. However, it often occurs that unexpected, abnormal abrasion scratches occur with the abraded material. In such cases, the problems occur in that the quality of the product cannot be kept good due to the occurrence of scratches.
The abrasive member of this type comprises a substrate and an abrasive layer, which is overlaid upon the substrate and comprises a binder and abrasive grains dispersed in the binder. The abrasive member has abrasion characteristics defined by various factors, such as grain diameter of the abrasive grains, surface roughness of the abrasive layer, and the kind of the binder.
It is required for the abrasive member to satisfy two requirements with respect to the abrasion characteristics in that the grinding power should be high and in that the surface smoothness of the abraded material should be good. However, the two requirements are incompatible with each other. Specifically, as for the conventional abrasive member provided with a single abrasive layer, the grain size of the abrasive grains contained in the abrasive layer is related to the abrasive power and the occurrence of scratches on the surface of the abraded material. For example, if abrasive grains having a large grain size are contained in the abrasive layer, a high abrasive power can be obtained, but more scratches will occur on the surface of the abraded material. If abrasive grains having a small grain size are contained in the abrasive layer, scratches will not readily occur on the surface of the abraded material, but the abrasive power will become low.
An abrasive member comprising a plurality of abrasive layers, which have different characteristics and are overlaid one upon another, is disclosed in, for example, Japanese Unexamined Patent Publication Nos. 6(1994)-79636 and 6(1994)-179174. In the disclosed abrasive member, an abrasive layer containing the abrasive grains having a large grain diameter is formed as the top layer, and an abrasive layer containing the abrasive grains having a small grain diameter is formed as a lower layer. A high abrasive power is obtained with the abrasive grains, which have the large grain size and are contained in the top layer. Also, cushioning characteristics are obtained with the lower abrasive layer, and the occurrence of scratches on the surface of the abraded material is thereby reduced.
Further, an abrasive tape comprising an abrasive layer, which contains the abrasive grains having a small grain diameter and constitutes a top layer, and an intermediate layer, which contains the abrasive grains having a large grain diameter and constitutes a lower layer, is disclosed in, for example, Japanese Unexamined Patent Publication No. 62(1987)-92205. In the disclosed abrasive tape, the abrasive grains, which have a large grain diameter and are contained in the intermediate layer, are constituted of soft non-magnetic grains having a Mohs hardness of approximately 1, such as talc powder.
As described above, with the abrasive member comprising the abrasive layer, which contains the abrasive grains having a large grain diameter and constitutes the top layer, and the abrasive layer, which contains the abrasive grains having a small grain diameter and constitutes the lower layer, a high abrasive power can be obtained. However, the abrasive member has the problems in that sufficient effects of restricting the occurrence of scratches cannot be obtained with the lower layer, and scratches occur to a certain extent on the surface of the abraded material.
Also, with the abrasive tape comprising the abrasive layer, which contains the abrasive grains having a small grain diameter and constitutes the top layer, and the intermediate layer, which contains the abrasive grains having a low hardness and a large grain diameter and constitutes the lower layer, the problems occur in that a desired surface roughness of the top abrasive layer cannot be obtained, and therefore a high abrasive power cannot be obtained.